Methods are already known for converting the Si-bonded alkoxy in organosilicon compounds to the dimethylsilyl group --O--Si(CH.sub.3).sub.2 H using 1,1,3,3-tetramethyldisiloxane H(CH.sub.3).sub.2 Si--O--Si(CH.sub..sub.3).sub.2 H. Thus, Japanese Laid Open (Kokai) Patent Application Number Hei 4-323222 teaches the reaction of alkoxysilane and 1,1,3,3-tetramethyldisiloxane in aqueous hydrochloric acid solution. Japanese Patent Application Hei 10-29297 (29,297/1998) teaches the reaction of alkoxysilane and 1,1,3,3-tetramethyldisiloxane in the presence of a carboxylic acid and a perfluoroalkanesulfonic acid. The former method suffers from a low conversion in the dimethylsilylation reaction, resulting in the presence of a fair amount of residual alkoxy in the organosilicon compound product. The latter method does provide a high conversion in the dimethylsilylation reaction, but cannot give the target product in high yields due to the occurrence of secondary reactions. These methods have thus been unable to produce SiH-functional organosilicon compounds in high purities from Si-bonded alkoxy-functional organosilicon compounds.
An object of the invention is to provide a method for preparing organosilicon compounds that can convert the Si-bonded alkoxy group to the diorganosilyl group at high conversion ratios and that can do so without the occurrence of secondary reactions. Another object of the invention is to provide a method for preparing a high-purity carbosiloxane dendrimer with a narrow molecular weight distribution through the use of the preceding method.